As a comment suggests, lasers have had negative temperature for decades. Infinite temperature has all energy states of a system populated in proportional to some bizarre quantum statistical numbering scheme. Positive temperature has lower energy states disproportionately occupied, negative temperature has higher states occupied. Traditional lasers rely on an excess of electrons in high energy states.

I don't understand any of that but it seems to me that if 'absolute zero' is the term for the lowest possible temperature and someone gets below that, then shouldn't 'absolute zero' be redefined with the new value?

Slaxl:I don't understand any of that but it seems to me that if 'absolute zero' is the term for the lowest possible temperature and someone gets below that, then shouldn't 'absolute zero' be redefined with the new value?

No, because the new value seems to be some kind of new state beyond no atomic motion (which is absolute zero) so the negative designation makes sense.

Slaxl:I don't understand any of that but it seems to me that if 'absolute zero' is the term for the lowest possible temperature and someone gets below that, then shouldn't 'absolute zero' be redefined with the new value?

Do not think of it as below, but rather opposite.

In the article they state "objects with negative temperatures are always hotter than ones with positive temperatures.".

Slaxl:I don't understand any of that but it seems to me that if 'absolute zero' is the term for the lowest possible temperature and someone gets below that, then shouldn't 'absolute zero' be redefined with the new value?

Absolute zero is defined as the cessation of all molecular motion. While I'm not sure how they did this, they circumvented that scale somehow.

doglover:Slaxl: I don't understand any of that but it seems to me that if 'absolute zero' is the term for the lowest possible temperature and someone gets below that, then shouldn't 'absolute zero' be redefined with the new value?

No, because the new value seems to be some kind of new state beyond no atomic motion (which is absolute zero) so the negative designation makes sense.

It's like backwards entropy, fizzy lifting drink for the density of occupied states.

QuantuMechanic:doglover: Slaxl: I don't understand any of that but it seems to me that if 'absolute zero' is the term for the lowest possible temperature and someone gets below that, then shouldn't 'absolute zero' be redefined with the new value?

No, because the new value seems to be some kind of new state beyond no atomic motion (which is absolute zero) so the negative designation makes sense.

It's like backwards entropy, fizzy lifting drink for the density of occupied states.

[xroads.virginia.edu image 640x480]

Also it's not the macroscopic temperatue, but a mathematical one. A better explanation to a layperson would be "It's just math. If you want the blunt skippy, go bone up on your basic quantum physics. If you don't fall asleep in ten minutes, I'll try to answer your question."

Negative temperature is not a new phenomenon, in lasers it's called "Population inversion" and it's how you get lasers to do their thing.

Think of it in terms of gravity. If you have gravity in one direction, you can call it "positive" gravity, and you're pulled towards the Earth. If you have "zero" gravity, you're not pulled anywhere, and just float. If you have "negative" gravity (anti-gravity), you are pushed away from the Earth. This doesn't mean you are feeling less force than the zero gravity situation, just that the force is pointing the other direction than you designated positive gravity.

Similarly, negative temperature is when the particles naturally settle uphill, rather than downhill, as it were.

Reading that article makes me think "This is what it's like to get old. I read the article, and the words make sense, but conceptually I just can't wrap my head around it. Confounded iPod3MP player device."

Yeah, lasers, basically, but these guys seem to have done it in a different system with some interesting effects.

The "easiest" way I've been able to understand this is they've created a system where adding energy serves to decrease the systems entropy. So they've created a roughly macroscopic system that exhibits that property. Which is pretty "cool".

"A substance with a negative temperature is not colder than absolute zero, but rather it is hotter than infinite temperature." actually seems like it makes more sense to me...

Negative temperature is not a new phenomenon, in lasers it's called "Population inversion" and it's how you get lasers to do their thing.

Think of it in terms of gravity. If you have gravity in one direction, you can call it "positive" gravity, and you're pulled towards the Earth. If you have "zero" gravity, you're not pulled anywhere, and just float. If you have "negative" gravity (anti-gravity), you are pushed away from the Earth. This doesn't mean you are feeling less force than the zero gravity situation, just that the force is pointing the other direction than you designated positive gravity.

Similarly, negative temperature is when the particles naturally settle uphill, rather than downhill, as it were.

I get the feeling that these 'below absolute zero' temperatures don't really exist. They are just part of the math in our currently less than perfect model for how the universe behaves. Measuring the temperature of a laser is meaningless since a laser is just photons and photons have neither mass nor temperature (although they can influence both of those characteristics in other bodies). Using a 'negative temperature' balances the math to make our model work.

Cave Johnson here. Those test subject wishing to make MORE than $60, and dont mind us flipping your molecular state to one where cold objects become hotter, in the name of SCIENCE, go see the nurse on level 10. And please, before you go, wash any flammable grease out of your beards.

ISO15693:Cave Johnson here. Those test subject wishing to make MORE than $60, and dont mind us flipping your molecular state to one where cold objects become hotter, in the name of SCIENCE, go see the nurse on level 10. And please, before you go, wash any flammable grease out of your beards.

Bad news, test subjects. The Temperature Inversion test has been cancelled. We do, however, have a new test for you, testing Microwave Ray Emitters against abominable ice monsters. Grab a weapon from the racks on level 9 and follow the blue line down the stairs to level 10. You'll know when the test begins.

Negative on the Kalvin scale does not mean below zero energy. Absolute zero means there is nothing moving because there is no classical energy. Mainstream media shouldn't report on physics news because they don't understand it.

"Let's expend an extraordinary amount of energy to align atoms into a state wherein we can use them to produce more energy!"

I'd be very interested to see how it ultimately shakes out, but my first instinct on this is that given the expense (energy wise) of using lasers in a vaccuum static environment in order to attain the states they have means that there's no way they get more energy out of the system than they put in it.

You can do all manner of entertaining things with math, but going from what they've achieved to 'heat engines that are more than 100-percent efficient' in more than a theoretical model still seems pretty absurd.

palelizard:ISO15693: Cave Johnson here. Those test subject wishing to make MORE than $60, and dont mind us flipping your molecular state to one where cold objects become hotter, in the name of SCIENCE, go see the nurse on level 10. And please, before you go, wash any flammable grease out of your beards.

Bad news, test subjects. The Temperature Inversion test has been cancelled. We do, however, have a new test for you, testing Microwave Ray Emitters against abominable ice monsters. Grab a weapon from the racks on level 9 and follow the blue line down the stairs to level 10. You'll know when the test begins.

Both of you receive 1/2 internet each for taking an old joke and making me laugh at it all over again.

madgonad:Measuring the temperature of a laser is meaningless since a laser is just photons and photons have neither mass nor temperature (although they can influence both of those characteristics in other bodies).

No, photons have energy, and a thermal distribution of photon energies corresponds to a temperature. The whole blackbody radiation thing happens when a photon gas is in thermal equilibrium with matter, i.e. they have the same temperature.

The weird part, as near as I can figure it, is that this "negative temperature" thing isn't the sort of temperature we're used to thinking about. Most of the time, we use temperature to describe the average energy of a bunch of particles. That has an absolute, inviolable zero: when the system of particles is in its lowest possible energy state.

The temperature they're talking about here isn't based on the average energy, but on the distribution of the various particles' energies. More low-energy particles than high-energy particles (which is how things settle down in equilibrium conditions) corresponds to a normal, positive temperature. More high-energy particles than low-energy particles requires a negative temperature to be plugged into the formula.

Energy distributions like that are non-thermal, i.e. they can't happen for a system that's in thermal equilibrium, but only when things are in flux somehow. Our normal concepts of temperature, heat flow, and such only apply to systems that are either in equilibrium or really close to it, so it's natural that applying them to other conditions produces screwy-sounding results. It's workable if you're meticulous about how things are defined, but you can see the sort of crap that happens when you let journalists loose on it.

ISO15693:Cave Johnson here. Those test subject wishing to make MORE than $60, and dont mind us flipping your molecular state to one where cold objects become hotter, in the name of SCIENCE, go see the nurse on level 10. And please, before you go, wash any flammable grease out of your beards.

ThreadSinger:ISO15693: Cave Johnson here. Those test subject wishing to make MORE than $60, and dont mind us flipping your molecular state to one where cold objects become hotter, in the name of SCIENCE, go see the nurse on level 10. And please, before you go, wash any flammable grease out of your beards.